Let's break this down. We're going to add 7509 and 2130 together.

Step 1: We'll start by adding the digits 9 & 0 in column 1 and get 9.

Step 2: We'll start by adding the digits 0 & 3 in column 2 and get 3.

Step 3: We'll start by adding the digits 5 & 1 in column 3 and get 6.

Step 4: We'll start by adding the digits 7 & 2 in column 4 and get 9.

So, 7509 + 2130 = 9639.

